In the June 1971 The Trader Speaks (from which I just posted an article about Crawford Foxwell's convention), editor Dan Dischley auctioned off a T206 Plank with a minimum bid of $150. The following month in the July issue, he announced that Bill Mastro had won it for $320. Mastro was 18 years old at the time. I'm not sure how close he was to the set at that point, but the following year he bought a Wagner for a then-record $1500 to complete his set. (See the profile of him from the January 1973 TTS in this thread:
http://www.net54baseball.com/showthread.php?t=217776.)